The number of Americans 65 years and older is expected to increase to ~20% (1 in 5) from the current ~13% (1 in 8) over the next two decades. Scientific research efforts for resolving aging physiology constitute an effective approach towards understanding, treating and preventing the development of cardiovascular disease; the number one killer of American citizens and culprit for diminishing quality of human life. Aging is associated with under-perfusion of vital tissues and organs with an integral role for vascular endothelial dysfunction. In resistance arteries that control blood flow into the microcirculation, the interaction of Ca2+ and electrical signaling pathways underlying endothelium-dependent vasodilation involves endothelium-derived hyperpolarization (EDH). Functional relationships support the initiation [e.g., activation of small- and intermediate-calcium-activated K+ channels (SKCa/IKCa)] and spread (via gap junctions) of hyperpolarization along and among the endothelium of network branches as a highly effective mechanism for coordinating tissue perfusion (i.e., oxygen delivery) with the metabolic demand of tissue parenchymal cells. Whereas aging is associated with oxidative stress (e.g., hydrogen peroxide production by mitochondria), there is a paucity of aging research concerned with EDH in the context of endothelial dysfunction underlying impaired tissue perfusion. Therefore, the goal of this project is to determine how mitochondrial-derived oxidative stress during aging interacts with endothelial cell Ca2+ and electrical signaling pathways that govern vasodilation and functional hyperemia. I will test the central hypothesis that the interaction of mitochondrial-derived Ca2+ and oxidative stress alter electrical signaling in the endothelium of microvascular resistance arteries. To investigate these relationships, I will employ a novel preparation of intact microvascular endothelial tubes, whereby freshly-dissected superior epigastric arteries of mouse abdominal skeletal muscle are treated to remove smooth muscle cells, adventitia, perivascular nerves and blood flow. Using intact endothelial tubes (length: ~3 mm, width: ~60 ?m) isolated from of Young (4-6 month), Intermediate (12-14 month), and Old (24- 26 month) C57BL/6 mice, I will employ simultaneous optical measurements of key signaling events (e.g., intracellular Ca2+ and H2O2 production) with intracellular recordings of membrane potential (Vm). Aim 1 will determine the mechanism by which oxidative stress alters endothelial Vm via activation of (SKCa/IKCa) with advancing age. Aim 2 will determine the role of mitochondria in Ca2+ buffering to impact (SKCa/IKCa) for ensuing hyperpolarization with advancing age. Aim 3 will determine mitochondrial production of reactive oxygen species and evaluate its role governing Vm in old age. This project will uniquely determine the role of mitochondrial handling of Ca2+ and oxidative stress signals in native intact microvascular endothelium. Results from this project will provide critical new insight towards developing therapeutic strategies for reversing endothelial dysfunction to promote tissue blood flow and sustain the quality of life during aging.